Radiotelephony



L. DE FOREST.

RADIOTELEPHONY.

APPLICATION FILED MAR. n, I915.

Patented Aug. 26, 1919.

D s Ares PATE OFFICE.

LEE Di: FOREST, OF NEW YORK, N. Y.,. ASSIGNOB TO DIE FOREST RADIO TELEPHONE AND TELEGRAPH COMPANY, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE.

immo'rnnnrnoiw.

' i This invention relatesto radio telephony.

.The object of the invention is to p-rovlde improved means for efliciently varying the high frequency energy employed in wireless telephoxntyi in accordance with sound waves.

A fu er object of the invention is to provide a system of radio telephony whereby the range of transmission and reception is shall be directl proportional to the changes increased.

I of high frequency ener radiated. The c ief di countered has been in. trying to vary the Other obj ectsof the invention will appear more fully hereinafter. I

It iswell known 111 radio telephony, and

particularly where it is desired to send messages through great distances, a large amount must necessarily be culty heretofore enlarge amounts of high frequency energy re- ?uired in accordance with the sound waves.-

n addition,- for successful operation for long range radio telephony, telephone transmitters or mlcrophones of such strength as to control from'lfl to 50 am'peres of current,and still retain their sensitiveness to voice vibrations have been necessary. Various metho'dsof constructing'and operating telephone transmitters to control the 'required current have ,heen proposed and tried, such as by employing a large number of carbon transmitters connected in series parallel ar- .rangement and cooling the same in various ways, but noneof the roposed methods have proved suificiently e cient. Either the heating and rapid destruction oi the transmitters or microphones results or the voice controlled devices are quite inadequate to control or to suflicintly -va large amounts of energy requir to permit --reception at great distances of the com arthe very atively slight current fluctuations .w 'ch these devices produce.

' For'long' distance-radio telephony it 'is necessary to produce variations in the amplitude' of the radiated wave-trains of from ,50

' a resistance-varyin to 100 per cent. of the total amount of energy.

received, and if it be -attempted to introduce device directly in the antenna-earth circu t of the transmitter sys- Specification of Letters Patent. Patented Aug. 26, 1919- Applicatlon filed March 11, 1915. Serial No. 18,573.

tern, this device must be capable of controlling from 10 to kilowatts of energy and of dissipating a very large percentage of this entire energy in heat.

It is among the special purposes of my 'present invention to provide arrangements for enabling long distance radio telephonic commumcations wherein it is not necessary to consume a large percentage of the normally radiated energy in volce actuated resistance devices, but merely to sufliciently alter the wave length of the radiated wavetrain to produce in the sharply tuned circuit at the'dlstant receiving station, changes in the amount of the energy received which .of inductance in the shunt circuit, and inversely proportional to the resistance of the microphone itself and its leads. This re-. vsistance, however, must be" kept comparatively low, as any ordinary microphone device which is capable of faithfully reproducing in resistance chan es the fluctuations of the voice can onl sa ely consume from 100 to 500 watts. owever, if the microhone 'be connected in shunt to too large an inductance, the potential drop' across its electrodes becomes so great that pernicious arcing occurs which not only rapidly. destroys the microphone but results in great distortion of the voice effects, and the device is apt to pack or cohere, in which case it ra idly becomes unresponsive to the voice, un ess special means are rovided to prevent this result. If, on the ot er hand the microof the total inductance of the transmitter circuit, the foregoing harmful effects are avoided, but the effect then on the alteration phone is, connected across toosmall a part becomes too small to be erceptible at a distance even in the most ar'ply tuned receiving circuits. 1 I have, discovered, however, that by combining a number of such microphones or voice transmitting devices and connecting each of them directly in" shunt across a small ortion of the total inductance and-actuating all of these microphones.

effects upon the transmitter devices'themselves, and to thus produce lar e fluctuations in the energy received by a distant sharply -tuned receiving system, in close simulation alternative transmitting arrangements em .a diagrammatic illustration of a mouthof the. original voice, or sound waves.

Various arrangements-for carrying out my discovery in practice may be employed,

and in the accompanying drawings I have shown various arrangements for accomplishin the desired results.

eferring to the drawings, Figure 1 shows a simple diagrammatic arrangement embodying my invention.

Fig. 1 is a view showing one form of a sharply tuned receiving system.

Figs. 2, 3, ands show diagrammatically bodying my invention.

The same part is designated by the samereference numeral through the several yiews.

Referring to Fig. 1, I have shown an ex ceedingly simple arrangement for accomplishing the objects and purposes of my inven'ti n wherein I employ the usual radiating antenna 1 ofia transmitting system which is connected to ground 2 through the usual variable load inductance 3 and the source of high frequency energy, indicated in this instance at 4. In this formof my invention I propose to employ an dditional inductance 5 which is of from 3 to 5 per cent. of the totalinductance in the antennaearth circuit. Three of more microphone transmitters, according to the number of turns employed in the additional inductance 5, designated at 6, are each connected'across a proportional amount of the inductance 5. In this case, where three microphones are employed, each one of them is connected across one third of the total inductance of the acoil 5. Reference numeral 7 designates piece as ge 'erally employedv in telephonic apparatus in' io which are delivered the sound I .waves to be reproduced at the distant sta ner,' and a small stopping condenser 11 is vconnected-in series between the antenna con.-

tion. These sound waves, in the arrangement shown, influence or affect to equal ex tent the micro hon'es 6.

In Fig. .1 have shown one form use in connectionwith my inventionwherein ble capacities and earth or ground of a well 10, is connected across the coupling.

denser 8, in the usual and well known mannection and the grid element-of the audion. 13 and 14 designate the two usualbatteries 0f the audion wing and filament circuits, 12'

of a sharply tuned receiving circuit suitable for, 7

3,8, 9, 2 are thefante'nna, inductance, variconnected in the wingjgr plate circuit-.of the audion, preferably tween the .Wing or plate "and the'battery 13-, as diagrammati:

.cally'illustrated at 15.

In Fig. 2 I have shown a transmitting system similar-to Fig. 1 where n the microphone transmitters are connected across the equal portion of the auxiliary inductance 5, but the diaphragms 16 0f the microphones ;are each actuated by an electromagnet 17.-

The C01lS'Of these electromagnets may-be connected in'- any desired relation. .1 have shown themcon'nectedinlseries with each other and in series with a variable-condenser 18 and with an' alternating current generator 19, having a frequency above that of the more essential frequency of the sound waves of the human voice. 2 It. is evident that when the inductance and capacity of the circuit 19, 18,17, aremade such that its natural period coincides "with that of-tlie frequency of the alternating current enerator 19, the diaphragms 16 aremaintained in continuous rythmic' vibration or fluctuation in the frequency and amplitude of the radiated waves, but at a rate too high to produce a disturbing sound in the telephonic receiver at the distant receiving station. This periodic agitation of the microphone devices 16,

17, prevents them from packing and at the same time greatly facilitates the control of the amplitude of their vibrations by means of the sound waves directed against the -master microphone transmitter, indicated at 20. This master microphone 20, isconnected in shunt across the 'en'erator 1,9', or across the. electro-magnets 1 as shown.

' In Fig. 3 Ihave shown the usual antennaearth system shown and described in' con nection with the preceding'figures, and a series of sensitive'conducting gas flames 33 is arranged to play between the fixed electrodes-31, 32, which are connected to their respective coils of the inductance 3, thereby making the air gaps between the electrodes 31, 32, 9. conducting medium and tending to short -circuitfthe coils ofthe inductance 3.

shown, these gas burners may be supplied from a common source through a tube 34. Thegas passes through. a small-chamber 35 one side of whichis closed b a flexible diaphragm 36 against which the sound waves of the voice 'orsound source is directedthrough the usualniouth piece 7.

In Fig.4'I' have-shown the. usual trans:

mitting. antenna-earth system with the auxiliary inductance 5 wherein the voice controlled resistance devices are mercu yapor discharge tubes 46, each -connec'te across one turn of the auxiliary inductance 5eat the base of the antenna-earth system. The vapor columns are deflected, and the resistance of the shunting circuits thereby altered.

by means of the electrom'agn'ets 17, placed in prozgimity to the discharge tubes, and opcrating as described in Fig. 2, the solenoids I being shown in this instance as connected in series and inseries with a source of current 50 and the master microphone 20.

' While I have shownmercury vapor tubes, my invention is not to be limited or restricted in this respect.

' It will be seen that I have supplied a means and apparatus for use in radio telephcountering .the

ony that permits the alteration of the wave length of the radiated wave trains at the transmitting station to producechanges in theainount of energy received at a distant receiving station which are directly proportional tothe changes in the resistance of the voice orsound actuated devices at the sending station, and it is obvious that it is thereby possible tov send telephonic communications over 'very great distances" without endisadvantages or objections that heretofore so far as applicant is aware has made'long distance telephonic commu'm- J cation unsatisfactory and expensive. 1 Having now set down the nature and purposes of my lnventlon, and

rangement for accomplishing the objects and embody ng my invention, what I claim as new anduseful and desire to secure byLet- .ters' Patent of the United States, is,--

1. In a radio telephonetransmitting system,Z- an inductance and aplurality of resistance varying devices, each connected in shunt around a relatively small portion of said inductance and means for simultaneouslymaintaini'ng all of said resistance varying devices in continuous vibration.

2. In a radio telephone transmitting system, an. inductance and a plurality of resistance varying device s, each connected in shunt around a relatively small portion of 'ous vibration.

having shown, and described variousmeans and c1rcu1t ar- In testimon said inductance and asource of alternatin current to simultaneousl maintain all 0 said resistance varying eyices in continu- 3. In a radio telephone transmitting system, an inductance and a plurality of resistance varying devices, each connected in shunt around a relatively small portion of said inductance and means including a source of alternating current having a frequenc above that of the more essential frequenciesof the human voice, for maintaining sa1d resistance varying devices in continuous vibration.

4. In a radio telephone transmitting system, an inductance and a plurality of re;

sistance varying devices, each connected in shunt around a relatively small portion of said inductance and means including a tinuous vibration and means for controlling the amplitude of said alternating current by sound waves.

whereof I have hereunto set my handin t e presence of the subscribing witnesses, on this 2nd day of March A.D.,

. I LEE on FOREST. Witnesses MARJORIE A. Gnsnvli, SAMUEL E. DARBY, Jr. 

